Field of the Invention
The present invention relates to a method of manufacturing an element substrate for ejecting liquid.
Description of the Related Art
A liquid ejection device for ejecting liquid such as ink to record an image on a recording medium generally has a liquid ejection head mounted thereon that includes an element substrate.
As a mechanism for ejecting liquid from the element substrate, one using a pressure chamber that contracts through the action of a piezoelectric element is known. In an element substrate having such a mechanism, a wall of the pressure chamber is a diaphragm. Through application of a voltage to the piezoelectric element leading to deformation of the piezoelectric element, the diaphragm warps, and the pressure chamber contracts and expands. The contraction of the pressure chamber applies a pressure to liquid in the pressure chamber, and the liquid is ejected through an orifice communicating with the pressure chamber.
A supply path is formed in the element substrate, and the liquid is supplied from the supply path to the pressure chamber. The supply path has a cross section perpendicular to a flow direction of the liquid (hereinafter referred to as “flow path cross section”) that is smaller than a flow path cross section of the pressure chamber, and functions as a flow reducing portion. It is known that usage of the supply path as a flow reducing portion maintains a certain level of a flow path resistance of liquid that flows into the pressure chamber to stabilize ejection characteristics of the element substrate.
In recent years, a liquid ejection device that can render an image at a high speed is required. In order to render an image at a high speed, it is necessary to shorten an ejection cycle of each pressure chamber. It is proposed that, as the ejection cycle is shortened, a volume of the liquid related to the ejection, that is, a capacity of the pressure chamber, is reduced to reduce a compliance of the liquid. The reduction in compliance increases a natural frequency of the pressure chamber, and thus, even if the ejection cycle is shortened, the liquid can be ejected with efficiency.
Further, a structure is known in which the flow path cross section of the flow reducing portion is further reduced along with downsizing of the pressure chamber (Japanese Patent Application Laid-Open No. 2012-532772). In an element substrate disclosed in Japanese Patent Application Laid-Open No. 2012-532772, a flow reducing portion and a pressure chamber are formed between a diaphragm and an orifice forming member. Reducing a distance between the diaphragm and the orifice forming member reduces the flow path cross section of the flow reducing portion and the capacity of the pressure chamber. Therefore, a frequency response of the pressure chamber can be improved without loss of stability of the ejection characteristics of the element substrate.
According to a technology disclosed in Japanese Patent Application Laid-Open No. 2012-532772, the pressure chamber and a flow inlet and a flow outlet that function as a flow reducing portion are formed by filling holes formed in a silicon layer on the diaphragm with the orifice forming member. A groove corresponding to the pressure chamber and a groove corresponding to the flow reducing portion are simultaneously formed by etching the silicon layer from a side opposite to the diaphragm. Therefore, a depth of the groove corresponding to the flow reducing portion is the same as a depth of the groove corresponding to the pressure chamber. In order to secure a flow path resistance of the flow reducing portion, a width of the groove corresponding to the flow reducing portion (that means a dimension of the groove in a direction perpendicular to the flow direction of the liquid and to a depth direction of the groove, and the same holds true hereinafter) is required to be smaller than a width of the groove corresponding to the pressure chamber.
It is relatively difficult to form a groove having a small width and a large depth, and the width of the groove tends to vary. Variations in the width of the groove lead to variations in the flow path resistance of the flow reducing portion, which affects desired ejection characteristics. From those reasons, a manufacturing method disclosed in Japanese Patent Application Laid-Open No. 2012-532772 requires processing of the silicon layer with higher accuracy, and thus, there is a problem of a low yield.